The present invention relates in general to aerodynamic drag reduction and, in particular, to aerodynamic drag reduction in kinetic energy projectiles.
Aerodynamic drag reduction is an important factor in improving the performance of projectiles. A substantial drag component for long-rod kinetic energy (KE) penetrators is the skin friction drag. This component is typically responsible for anywhere from a third to a half of the total drag.
The skin friction drag is affected by the characteristics of the flow pattern over the body. Exposed projectile body grooves, which allow a sabot to hold on to and drive a projectile, affect the flow and often create more drag than a smooth body would. Scientists have examined the effect and have created computer programs to predict groove drag components for various projectile configurations. Increases in drag, due to projectile grooves, can be on the order of 10% of the total drag for Mach numbers near 3.5. See Mikhail, A. "Incremental Drag Due to Grooves and Threads for KE Projectiles." BRL-TR-2982, U.S. Army Ballistic Research Laboratory, Aberdeen Proving Ground, Md., March 1989.
As increasing length-over-diameter (L/D) projectiles are required, the amount of grooves required to launch them may increase groove drag further. It is possible that covers could be fabricated that slide over the grooves once the sabot has discarded. Unfortunately, these covers would be required to move into position and lock in place. This would be a difficult task in a high Mach number environment and would likely involve substantial projectile modification, significant development costs, and time expenditures.
A system of flow modification using "intumescent" materials requires no moving parts, and is actuated by the free-flight temperature conditions. Additionally, it requires only minor projectile modifications.